*Correctio for the scenario * After we move fence_put(entity->last_sched) out of the fini_status check:
A potential race issue for the scenario: 1. Drm_sched_entity_fini(): it exit right after entity->job_queue empty, [ but that time scheduler is not fast enough to deal with this entity now ] 2. Drm_sched_entity_cleanup() : it call dma_fence_put(entity->last_scheduled) [ but this time entity->last_scheduled actually points to the fence prior to the real last one ] 3. Scheduler_main() now dealing with this entity: it call dma_fence_put(entity->last_scheduled) [ Now this fence get double put !!! ] 4. Scheduler_main() now call dma_fence_get() on the *real* last one ! So eventually the real last one fence triggers memory leak and more critical the double put fence cause NULL pointer access /Monk From: Liu, Monk Sent: 2018年4月18日 15:11 To: Koenig, Christian <christian.koe...@amd.com>; Deng, Emily <emily.d...@amd.com> Cc: amd-gfx@lists.freedesktop.org Subject: force app kill patch Hi Christian & Emily I think the v4 fix for “fix force app kill hang” is still not good enough: First: See that in “sched_entity_fini”, we only call dma_fence_put(entity->last_scheduled” under the condition of “If (entity->fini_status)”, so This way there is memory leak for the case of “entity->fini_stats ==0” Second: If we move dma_fence_put(entity->last_scheduled) out of the condition of “if (entity->fini_status)”, the memory leak issue can be fixed But there will be kernel NULL pointer access, I think the time you call dma_fence_put(entity->last_scheduled”) may actually executed *not* On the last scheduled fence of this entity, because it is run without “thread_park/unpark” pair which to make sure scheduler not dealing this entity So with certain race issue, here is the scenario: 1. scheduler is doing the dma_fence_put() on the 1st fence, 2. scheduler set entity->last_scheduled to 1st fence 3. now sched_entity_fini() run, and it call dma_fence_put() on entity->last_scheduled 4. now this 1st fence is actually put double time and the real last fence won’t get put by expected any idea? /Monk
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